Ocular conditions characterized by intraocular pressure, such as chronic open-angle glaucoma or secondary glaucoma, have been successfully treated by administration of methazolamide, and analogs and derivatives thereof. Methazolamide is a carbonic anhydrase inhibitor that slows the formation of excess fluids behind the cornea, by inhibiting a chemical reaction at the ciliary body.
Many prior art methazolamide compositions are administerable topically, directly to the eye. Such administration can be disadvantageous to individuals who prefer oral medications. Moreover, in topical applications, the concentration of methazolamide available to the affected tissue is difficult to regulate and maintain. The frequent necessity for re-application of topical methazolamide can be inconvenient and result in inconsistent efficacy.
Additionally, some prior art methazolamide compositions provide an oral dosage of methazolamide, but these compositions do not provide a consistent dosage of methazolamide over an extended period of time. Methazolamide is a water-insoluble, hydrophilic drug. Sustained release formulations of water-insoluble hydrophobic drugs tend to yield inconsistent drug release profiles which make it difficult to control in vivo absorption of these types of drugs in the intestines.
Various controlled release pharmaceutical formulations have been proposed in the prior art, however, none have proven economical for manufacture and satisfactory in drug release profiles. Also, some of these formulations include additional compounds, such as anionic surfactants, which are undesired. Prior art formulations of sustained release methazolamide tablets have only been achieved for dosages of methazolamide in the range of 25 to 50 mg per tablet. These prior art formulations of extended release tablets have used spherical granules of methazolamide, different types of binders, or additional compounds, but none have produced a consistent drug release profile for methazolamide having methazolamide dosages of 75 mg or more per tablet.
Prior art formulations of sustained release methazolamide tablets have used lower dosages of methazolamide, from 25 to 50 mg per tablet, in the form of spherical granules which are then tableted. While tablets comprising spherical granules are effective at these lower dosage amounts, it has been difficult to achieve or control the release of the drug in higher dosage tablets having these spherical granules. Thus, there are currently no available oral methazolamide compositions containing higher dosages, i.e. at least 75 mg, in a sustained release per diem formula. Due to the low dosages in the existing prior art formulations, the tablets must be taken several times a day, which may be problematic should the individual forget to take the oral dosage at the prescribed time. Therefore, there exists a need for a sustained release methazolamide composition that contains a higher dosage of methazolamide such that only one tablet per day is required to provide relief from intraocular pressure.
A sustained release oral dosage formula is therefore desirable to provide a therapeutic concentration of methazolamide over an extended period of time without the use of unnecessary compounds. The formula would be preferably chosen such that an individual only requires a single dosage per diem. This dosage would be preferably provided in an orally administerable tablet.